1. Field of the Invention
The invention relates to a hydraulic actuation arrangement, particularly for covers, doors, convertible tops and the like on vehicles, having at least one double-action working cylinder whose working chambers are in communication via a mutually unseatable check valve with one side of a reversible pressure medium source, respectively, whereby each working chamber is connected to a pressure medium source by at least one pressure-relief valve or pressurizing valve, and whereby at least one working chamber communicates additionally with a pressure medium reservoir through an additional pressurizing valve and a two-stage pressurizing valve. This configuration is especially used in an actuation arrangement to open and close a flow-through opening in a passage for the pressure medium, having a valve housing and a valve element slidably mounted therein, whereby the valve element is biased by a resilient element in the closing direction of the flow-through opening, and whereby on the resilient element there is a control connection provided through which the valve element is biased by a force in the closing direction as well.
2. The Prior Art
Arrangements of this type are well known and make possible, for example, automatic actuation of vehicle doors, hoods, maintenance access doors, trunk lids, or the cover of the space receiving a convertible top. It is guaranteed by the use of mutually unseatable check valves, which are for example described for pneumatic actuation devices in DE 43 34 843 A1, that during turn-off or malfunction of the operational pressure, the hinged covers remain hydraulically blocked in a particular position to prevent uncontrolled movement (of the component) and risk of injuries resulting thereof. The pressurizing valve enables controlled continued movement of the hinged cover by hand in this condition, for example, to thusly allow emergency closing against the force determined by the pressurizing valve. In AT 405 752 B1 there is also a similar configuration described in which however no precautions of any kind are offered to make available different force levels during the manual actuation process.
To achieve a reduction in the force necessary to move the component by hand in an emergency operation, which is otherwise actuated hydraulically, it has been proposed in DE 197 40 029 C2 to provide a pressure-relief valve with two different operational triggers so that after overcoming a first higher threshold value at the beginning of the emergency operation, a lower pressure is subsequently necessary to keep the valve open and to manually bring the component into the desired position. Nevertheless, in this arrangement the valve element is continuously biased by the existing operating pressure in the opening direction and the first pressure threshold value must correspond to the maximal possible or desired system pressure, which leads to very high initial forces to overcome during emergency operation. Moreover, the two-stage pressurizing valve disclosed in DE 197 40 029 C2 is to be provided with a cylindrical stepped sealing element so that a considerably longer passage is necessary to the opening of the first higher pressure stage, which in turn makes necessary a longer influence of the higher force at the beginning of the manual actuation.
Two-stage valves are also very generally disclosed in DE 41 30 832 C1, wherein the two stages are however not disposed one behind the other and in the same flowthrough passage. In U.S. Pat. No. 5,916,628 a check valve is disclosed but no information is given about the force conditions before and after pressurizing by the valve, since only the flow-through cross section is of significance during the process of the opening movement. The safety check valve in U.S. Pat. No. 3,916,946 includes two independently functioning valve elements that are connected in series, but there is no information concerning a controlled movement sequence or different pressure stages.
It is therefore the object of the present invention to provide an improved arrangement of the type described above wherein the manual force necessary during emergency operation may be clearly reduced at the start of the manual movement as well as during the movement, whereby these force levels may be selected for both movement directions independently from the maximum system pressure and the force levels may also be selected independently in consecutive sequence. However, an additional object of the present invention is also a two-stage pressurizing valve which safely guarantees by simple fabrication the keeping of both pressure threshold values and which makes the transfer between the two switching stages possible in a rapid manner.
The first object is achieved according to the invention in that the hydraulic actuation arrangement described above is provided with at least one additional pressurizing valve and at least two different threshold values. The forces for emergency operation are given by the pressure threshold values of the second pressurizing valve, whereby the higher value may correspond to the highest system pressure at the most, but which is preferably considerably lower. The higher pressure threshold value is preferably selected in a way whereby the normally hydraulic actuated component is safely fixed exactly in each positionxe2x80x94its own position and that of the vehiclexe2x80x94and whereby a force exceeding the holding force only by a small degree is sufficient for displacement from this position. After introduction of the manual movement there is only a force necessary to continue the movement, which is given by the second lower pressure threshold value of the second pressurized valve. This advantageous force reduction may be in the most simple application be provided only for one movement direction, but it may also be achieved of course for both movement directions of the normally hydraulic actuated component in that both working chambers are respectively connected to the pressure reservoir via at least one common pressurizing valve, preferably via a respective dedicated (own) pressurizing valve.
The pressure threshold value for opening of the additional pressurizing valve is thereby preferably higher than the pressure threshold value to keep the valve in an open position.
Each working chamber is connected with the pressure means reservoir through its own pressurizing valve according to the invention to achieve, independently from one another, an adjustment of the actuation forces in the opening and closing direction.
In both above-mentioned cases it is also conceivable that two separate pressure relief valves exist for the maximum system pressure, one for the outward movement of the working cylinder and one for the inward movement. Thereby the pressure threshold values are then set maximally as high for the respective second pressurized valve as the threshold values of the pressure relief valve connected on that side of the working cylinder.
In working cylinders with a different cross section at the piston-side or rod-side it is preferably proposed that in order to obtain volume compensation, the piston-side working chamber of the working cylinder is connected with the pressure medium reservoir via a line having a check valve blocking toward that pressure medium reservoir.
The second object of the present invention is achieved by a pressurizing valve which is characterized in that there is a flow-through opening provided that may be blocked by the valve element whereby the surface area of the flow-through opening is smaller that the cross section area of the valve element, and whereby the front end of the valve element controlling the flow-through opening is designed in a cone-shaped manner. Through the cooperation of the valve seat (defined by the flow-through opening) with the valve cone of the valve element, an optimum sealing effect on the shoulder of the valve seat is obtained to guarantee the transfer between the two pressure threshold values as quickly as possible, which are given by the different pressure applied to the surfaces (entire valve conexe2x80x94lower pressure threshold value; cross section of the valve seat higher pressure threshold value.)
It is preferred that the front end of the valve element sealingly cooperates with the shoulder of the flow-through opening metal-to-metal and whereby the valve element, and preferably the second flow-through opening, are sealingly guided in the valve housing metal-to-metal as well.
According to an additional characteristic of the invention, a piston is provided for hydraulic blocking of the pressurized valve whereby the piston is urged toward the end of the valve element, which is disposed at the opposite end of the shoulder of the flowthrough opening, by means of pressure applied at the control connection.